2.2.1. Treatment 1: wave barrier fence
A wave barrier fence (Fig. 4a) was set up 60 m offshore from the
dyke. It consisted of two parallel rows of Melaleuca poles with
0.5–1 m gap between them. Large poles (>5.5 cm in diameter;
Table 1) were used to construct the landward fence. A post driver
was used to push the poles 3.0–3.5 m into the mud with 1.5–2.0 m
remaining above the substrate to establish a fence of poles for wave
and wind resistance. Gap between adjacent poles was approxi-
mately 10 cm meaning that six thousand large poles were needed
to construct 1 km of fence. The seaward fence was constructed with
smaller poles (pole 4 or 5; Table 1) sunk 2.0–2.5 m into the mud. A
larger pole positioned in every 1.5 m was included in the seaward
fence to help resist wave action. One kilometer of sea ward fence,
required approximately 13,000 pole 4 and 340 large poles. Bamboo
matting (1.0–1.2 m high, 1.5 m long) and
fine
fishing net (1 m high,
3–5 m long) were attached to the inside of the seaward fence. After
attaching the bamboo mat and
fishing net, tree branches and small
diameter poles (0.5 m3) were added into the gap between the rows.
The bamboo mat and
fishnet needed to be supplemented annually
for up to 3 years to maintain a functional fence. The construction
cost of the wave barrier fence is US$21,000/km with annual
maintenance costs of US$4200/km.